The present invention relates generally to microwave excited ultraviolet lamp systems and, more particularly, to an exhaust system for directing cooling air used in such lamp systems.
Ultraviolet lamp systems, such as those used in the heating or curing of adhesives, sealants, inks or other coatings for example, are designed for coupling microwave energy to an electrodeless lamp, such as an ultraviolet (UV) plasma lamp bulb mounted within a microwave chamber of the lamp system. In ultraviolet lamp heating and curing applications, one or more magnetrons are typically provided in the lamp system to couple microwave radiation to the plasma lamp bulb within the microwave chamber. The magnetrons are coupled to the microwave chamber through waveguides that include output ports connected to an upper end of the chamber. When the plasma lamp bulb is sufficiently excited by the microwave energy, it emits ultraviolet radiation through an open lamp face of the lamp system to irradiate a substrate which is located generally near the open lamp face.
A source of pressurized air is fluidly connected to a housing of the lamp system which contains the magnetrons, the microwave chamber and the plasma lamp bulb. The source of pressurized air is operable to direct cooling air, such as 350 CFM of cooling air for example, through the housing and into the microwave chamber to properly cool the magnetrons and the plasma lamp bulb during irradiation of the substrate by the lamp system.
In some UV heating and curing applications, the lamp system includes a mesh screen mounted at the open lamp face which is transmissive to ultraviolet radiation but is opaque to microwaves. The configuration of the mesh screen also permits the significant air flow of cooling air to pass therethrough and toward the substrate.
In some applications, however, the substrate may require a clean environment, such as in a curing chamber, so that the substrate will not be contaminated during the heating and curing process by contaminants carried by the cooling air in contact with the substrate. The substrate may also be somewhat delicate and therefore susceptible to damage in harsh environments, such as under the influence of the significant air flow of the cooling air which impinges upon and possibly disturbs the substrate. Oftentimes, the substrate may also be adversely affected by excessive heat which may be generated by the plasma lamp bulb during the irradiation process.
Accordingly, there is a need for a microwave excited ultraviolet lamp system which may be used in a clean environment to prevent contamination of a substrate by the cooling air necessary to properly cool the lamp system. There is also a need for a lamp system which reduces or eliminates the potential damage to a substrate by the significant air flow of cooling air used to cool the lamp system. There is yet also a need for a lamp system which minimizes heat transfer from the plasma lamp bulb to the substrate being irradiated.
The present invention overcomes the foregoing and other shortcomings and drawbacks of heretofore known exhaust systems for microwave excited ultraviolet lamp systems. While the invention will be described in connection with certain embodiments, it will be understood that the invention is not limited to these embodiments. On the contrary, the invention includes all alternatives, modifications and equivalents as may be included within the spirit and scope of the present invention.
According to one aspect of the present invention, a microwave excited ultraviolet lamp system or light source is provided having an exhaust system mounted thereto in accordance with the principles of the present invention. The light source includes a housing which is connected to a source of pressurized air which is operable to direct cooling air through the housing and into the microwave chamber to cool the magnetrons and plasma lamp bulb of the light source.
The exhaust system of the present invention is mounted in fluid communication with the light source and is configured to contain and direct the cooling air emitted by the lamp source so as not to contact the substrate being irradiated with ultraviolet light. The exhaust system comprises an enclosed exhaust duct having an air inlet port configured to receive the cooling air emitted from the light source and an air exhaust port configured to direct the cooling air within the exhaust duct to a location remote from the light source so that the cooling air does not contact and thereby possibly contaminate or disturb the substrate.
A lens, such as a quartz lens, is supported by the exhaust duct and is operable to transmit the ultraviolet light emitted from the light source toward the substrate. The quartz lens is beneficial to reduce heat transfer to the substrate from the plasma lamp bulb and also serves as an air shield to prevent the cooling air from contacting the substrate.
In accordance with another aspect of the present invention, a sensor, such as a differential pressure transducer, is provided within the housing of the light source to insure that a sufficient cooling air flow rate is being provided for proper operation of the magnetrons and the plasma lamp bulb. The pressure transducer senses the pressure drop between the interior of the housing and the exhaust system and provides a signal to a control of the light source to shutdown operation when the desired pressure drop is not sensed by the pressure transducer.
The above and other objects and advantages of the present invention shall be made apparent from the accompanying drawings and the description thereof.